Process for producing perchlorethylene



Jan. 16, 1951 o. FRUHWIRTH ET AL 2,538,723

PROCESS FOR PRODUCING PERCHLORETHYLENE Filed July 28, 194'? I, COLD WATER VAPORS Cl RASCHIG RINGS l ,COOLER COOLING FLUID CRUDE c 01 Erc.

TH ERM OSTAT (l VOL.)

ryizztm %ML;AZZ 9L HMJ Waflw PERT-K r CALM m WW Patent ed Jan. 16, 1951 PROCESS FOR PRODUCING PEBCHLOR- ETHYLENE om Fruhwirtli and Heinrich Walla, Bruckl, Carinthia, Austria, assignors to Donau Chemie Aktiengesellschaft, Vienna III, Austria Application July 28, 1947, Serial No. 764,050 In Germany August 6, 1940 Section 1, Public Law 690, August s, 1940 Patent expires August 6, 1960 6 Claims. I

This invention relates to an improved process for the production of perchlorethylene,

Perchlorethylene has been produced till nowv so far as made from acetylene, according to complicated technical processes. Acetylene has been an inert gas such as gaseous hydrochloric acid.

This mixture was conducted. over'hot contacts at temperatures of about 250-400? C. By cooling the reaction gases, perchlorethylene wasobtained besides other chlorinated hydrocarbons.

We have now found that perchlorethylene can also be obtained with a very good yield by burning acetylene and chlorine in one working step. The process according to our invention consists in burning an intimate mixture of about one part by volume of acetylene and 3 to 3.5 parts by volume of chlorine, in the form of a flame. The combustion chamber in which this flame is produced may be, as shown in the accompanying drawing, a vertical cylindrical, tubular chamber, having a diameter substantially larger than the diameter of the flame, and the gas mixture may be introduced in an upward direction through piping located at the bottom of said combustion chamber.

The temperature in the reaction zone should rise slowly, measured from the entrance of the gaseous mixture into said reaction'zone, up to the point where the flame itself begins.

When the gaseous mixture is blown upwardly into the bottom of the combustion chamber, chemical reaction between the chlorine and the acetylene gives out a substantial amount of heat. The temperature of the gases below the flame may rise to nearly 600 C. When the temperature of the gases reaches about 600 C., the gases ignite (i. e. the flame itself begins). The temperature in the flame rises up to about 750 to 950 C. The final temperature of the hottest part of the flame depends on the quantity of gaseous mixture reacted and its composition.

The regulation of the rise of temperature in the reaction zone can be effected by different measures. It is essential, above all, that the speed of the gaseous mixture, when leaving the nozzle in order to enter the combustion space, he as great as possible. Preferably, it must be blown in at a speed above 20 m./sec. in order to avoid the formation of by-products. By this great speed of the gaseous mixture, the reaction zone (flame) is necessarily extended so that there is a relatively slow rise of temperature between the point of arrival of the gas mixture into the reaction zone and the extreme end of the flame.

Another means in order to retard the rise of temperature, which is to be employed preferably in combination with the aforesaid measure, is to avoid a reflection of heat from the wall of the combustion space into the flame, especially into the first part of the reaction zone. To this effect, the walls of the combustion roommay be cooled throughout their whole length or locally, but the cooling must be regulated so that there is no separation of intermediate products of a lower degree of chlorination upon the interior wall. Care is also to be taken that the distance between the wall of the combustion chamber and the flame islarge enough in order to maintain the latter stable. If this distance is large enough, it is not necessary to cool the wall.

Furthermore, the first part of the reaction zone can be cooled for instance by evaporating inert liquids, especially by pulverizing (e. g. atomizing) liquid reaction products, such as perchlorethylene. The pulverization is preferably effected by means of the gaseous mixture coming out of the nozzle.

In order to avoid a further chlorination of the perchlorethylene obtained by combustion, which at lower temperatures would yield higher percentages of hexachlorethane, especially when employing greater quantities of chlorine, care must be taken that the chlorinated hydrocarbons be cooled nd condensed to the largest possible extent.

Cooling may be effected by any suitable technical means. For instance, the reaction gases may be conducted into a gas cooler. It has proved to be of special advantage to bring the reaction gases into contact with water. The hydrochloric acid formed by the combustion is thereby absorbed and the chlorinated hydrocarbons are simultaneously condensed. Perchlorethylene which is insoluble in water, separates as a layer.

According to our new process, perchlorethylene can be produced in a continuous manner with a, yield up to -85%. Furthermore, in conhexachlorethane/tetrachlormethane, at the corresponding combustion temperature about 2% of hexachlorethane and 7-9% of tetrachlormethane are formed by further chlorination. Owing to the special measures described, the decomposition and the polymerization of acetylene is avoided, whereas the formation of hexachlorbutadiene and hexachlorbenzene, which generally takes place at the same time, is retarded to a large extent.

For the process according to the invention, no catalyser is needed. Our new process for producing perchlorethylene is therefore much less sensitive to impurities contained in the reaction'gases than the known process in which acetylene and chlorine are reacted in the presence of a catalyzer at'temperatures of about 250-400 C. It is therefore to be regarded as a, special advantage of our process that also technical gas mixtures containing acetylene and chlorine can be burned together with the formation of perchlorethylene. For instance, waste gases containing a substantial amount of acetylene can be reacted with pure chlorine or with waste gases containing the same or also mixtures of pure acetylene with waste gases containing chlorine may be burned together. If the gas mixture which is burned' contains other substances besides acetylene and chlorine which .account, so that always enough acetylene and chlorine are present for the formation of perchlorethylene. The concentration of these two gases in the mixture to be burned must be high enough to furnish enough heat so that the reaction will go on as a combustion. Eventually, acetylene or chlorine must be added (if an insufilcient amount of one is present) to the mixture prior to the combustion.

For a good yield of perchlorethylene, it is essential that gas mixtures are used which contain acetylene and chlorine in the proportion by volume of about 1:13-1:35. It more chlorine is used, the proportion of perchlorethylene in the final product decreases slowly and more hexachlorethane is formed. If less than 3 volumes of chlorine are used per one volume of acetylene, the yield of perchlorethylene diminishes and more hexachlorbutadiene is formed.

Compared with the known processes for producing perchlorethylene, our new process is distinguished by the simplicity of the method and of the apparatus to be used, by the fact that large amounts of the starting components may be reacted with each other per unit of time as well as by the possibility to use technical gas mixtures as starting components without any inconvenience.

Our invention is still illustrated by the following examples without, however, being restricted thereto.

Example 1 This mixture becomes sured in the liquid state) by the current of the gas mixture. In order to avoid a further chlorination of the perchlorethylene formed by the combustion, the combustion gases are cooled immediately after complete combustion. Then, the

greatest part of the chlorinated hydrocarbons is condensed. The remaining gases are brought into contact with water, for instance in an absorption tower. Therest of the chlorinated hydrocarbons is condensed and may easily be separated from the aqueous hydrochloric'acid obtained.

lill

The reaction product consists essentially of perchlorethylene. It may be purified in the usual manner.

Example 2 Through a gas-mixing nozzle are blown with a, speed of m'./sec. on the one hand 8 mfi/h. of a mixture of waste gases containing 50% of acetylene, 30% of nitrogen, 10% of carbon dioxide and 10% of hydrogen, on the other hand 14 mfi/h. of chlorine, into a combustion pipe of 30 centimeters diameter and of 3 meters length, the outer walls of which are cooled with water. The mixture is inflamed. The combustion pipe leads into a gas refrigerator, in which the gasesscoming out are cooled to room temperature. The greatest part of the perchlorethylene is condensed thereby, whereas the rest is separated (condensed), during the following absorption of the hydrochloric acid.

Example 3 An intimate gaseous mixture of 4 mfi/h. oi

acetylene and 23 mP/h. of a waste gas mixture having a content of 60% C12, 5% H2, 16% CO2,

16% N2 and 3% Oz is blown with a speed of 60 m./sec. into a combustion pipe of 25 centimeters diameter and 1 meters length, the outer walls of which are cooled with water. Then, the mixture ignites to form the flame. The perchlorethylene formed is separated from the combustion gases by cooling to 0 C. The hydrochloric acid formed during the combustion is employed elsewhere in mixture with the residual gases which no longer contain hydrogen.

While we have described our improvements in great detail and with respect to preferred embodiments thereof, we do not desire to limit ourselves to such details or embodiments, since many modifications and changes may be made and the invention embodied in widely difierent forms without departing from the spirit or scope of the invention in its broadest aspects. Hence we desire to cover all modifications and forms within the scope or language of any one or more of the appended claims.

In the practical performance of this process on a larger scale it was found that besides the main product perchlorethylene a small amount of lower or higher boiling products is formed which contaminates the main product. byproducts may be removed from the main product and if desired separately obtained by condensing the main product as fraction between 120 and C. out of the gas mixture produced by the combustion of acetylene and chlorine.

The separation of the main product and the byproducts, respectively, may be carried out in accordance with the invention in different ways. For example solid bodies maintained at temperatures approximately between and 80 C. may be provided within the chamber containing the combustion gases. However it is more suitable, to bring the combustion gases into contact with a fluid of the above mentioned These temperatures, which does not mix and does not react with them, for example sulphuric acid or phosphoric acid. Furthermore, the combustion gases may be washed for instance with a fluid miscible with the condensate, which preferably is a product of the combustion itself. Thus it is possible to eflect the separation of the: components boiling over 120 C. for example by irrigation of the combustion gases with liquid perchlorethylene. The gases are necessarily cooled by evaporation of a part of theaddediiquid perchlorethylene to approximately 120 C. The high boiling components especially hexachlorbutadiene and hexachlorbenzene, are dissolved by the part, of perchlorethylene which is not evaporated and suitably is circulating, or are enriched in it, but are precipitated after the cooling of the perchlorethylene nearly completely in coarse crystalline form and may be isolated in pure state.

The separation of the main product of the reaction. (perchlorethylene) as a. fraction boiling between 120-80? C. is for example attained by bringing the remaining gases into contact with solid bodies, or better with a fluid, not miscible and not reacting with the condensate, which bodies or fluids are kept at temperatures of about 78-80 C. The still remaining part of the gases is either cooled to room temperature, the components boiling below 80 0., especially carbon tetrachloride, being separated thereby or by irrigating the gases with cold water, the hydrochloric acid being absorbed thereby and simultaneously the reaction products boiling below 80 C. being condensed. However it isalso possible to condense the gaseous and vaporous reaction products in one step and to fractionate the condensate by distillation to separate the perchlorethylene from the byproducts.

The process according to the invention 'is described in the following with reference to the acompanying drawing showing an embodiment of a convenient apparatus for carrying out this process. By the valved pipe lines 2 and 3 acetylene and chlorine, respectively, in a proportion corresponding substantially to the ratio of about one part of volume of acetylene to about 3 to 3.5 parts by volume of chlorine are introduced into a mixing pipe I. After thorough mixing the gaseous mixture is discharged through a combustion nozzle 5 provided in the head of a burner 4 and ignited and burned.

The outside wall of the combustion chamber 6 is cooled with water supplied through a, perforated ring I and flowing oil from the collector 8. At times, some liquid may condense on the inside of 6, and may flow downwardly and out through 9a. The head of the burner l is cooled e. g. by means of the cooling Jacket 9 situated around it. The combustion gases pass from the combustion chamber to the column 10 containing Raschig rings which are irrigated with perchlorethylene introduced by a sprayer II. A part of the perchlorethylene introduced evaporates when meeting the hot combustion gases, another part flows 03 from the column I0 through a pipe l4 located v below the perforated plate l2. The components of the combustion gases boiling above 120 C. are thus condensed and removed from the perchlorethylene flowing off. The perchlorethylene not vaporized in H] is led in a liquid form, from the bottom of the perforated hood l3 and leaves the bottom of ill by a pipe line It. The high boiling components carried along with it are separated (solidlfled) by cooling (say with cold water) in II and are retained in solid state by a filter it. They consist essentially of hexachlorbutadiene and hexachlorbenzene. The perchlorethylene flowing out of the filter i6 is returned by a pump l'l through a reservoir l8 to the sprayer ii and again used for washing and cooling the combustion.gas.es-.

,The'separation of the perchlorethylene out of gases and vapors leaving the column 10 by a pipe line I9 may be effected in a similar way by circulating sulphuric acid in contact with the gases and vapors. The gases and vapors from i9 enter a column 20, filled with Raschig rings, through which warm sulphuric acid of Vii- C. trickles down from a sprayer 2|. By this measure the perchlorethylene is condensed and flows with the sulphuric acid out through a perforated plate 22 into a separator 23. The perchlorethylene flows off through an overflow 20 to storage, while the sulphuric acid in the bottom of the separator 23 flows of! by the pipe 25 and is returned to the sprayer 2| by means of a pump 26 througha thermostat 21 and a reservoir 28.

The condensation of the components boiling below 78-80" C. (C014 and HCl etc. is effected by introducing the gases leaving the column 20 by a pipe line 29 into an absorber 30, irrigated with cold water. The hydrochloric acid is absorbed in this water, and the carbon tetrachloride vapor is condensed in this absorber. The watery hydrochloric acid is allowed to flow off by the pipe line 3|, while the condensate collecting at the bottom (which may be largely carbon tetrachloride) is drawn ofi at 32.

' We claim:

l. A process of producing perchlorethylene which comprises burning an intimate mixture of acetylene and chlorine in the proportion by volume of about 1:3 to 1:35, in the form of a flame in which flame the temperature at the cooler end is about 600 C., and the temperature at the hottest part of the flame, l. e. at its end, is about 750 C. to about 950 C.

2. A process of producing perchlorethylene which comprises burning an intimate mixture of acetylene and chlorine in the proportions of about 1:3 and 1:35, in the form of a-flame the temperature of which flame, at its beginning is about 600 C. and the temperature of which flame increases to between about 750 C. and about 950 C., and in which process the mixture of acetylene and chlorine is blown into the combustion zone at a speed of more than 20 meters per second.

3. A process as in claim 1, in which the initial portion of the reaction zone is subjected to a cooling operation.

4. A process as in claim 1, in which an inert liquid is evaporated in the initial portion of the reaction zone, to effect a cooling.

5. A process as in claim 1, in which the products of combustion of the flame are then promptly subjected to a cooling operation.

6. A process as in claim 1, followed promptly by subjecting the products of combustion of said flame to washing with an excess of perchlorethylene, whereby all products having boiling points substantially above that of perchlorethylene are condensed from the gases.

O'I'IO FRUHWIRTH. HEINRICH WALLA.

(References on following page) 7 nu'mmcus mm The following references are of record in the file 0! this patent:

UNITED STATES PATENTS Number Name Date Johnson Sept. 27, 1887 Roka June 6, 1922 Roka Nov. 18, 1924 Porter Jan. 24, 1933 Reilly Dec. 20, 1938 Hennig May 30, 1939 Basel et a1. Nov. 7, 1939 Basel et a1. Sept. 6, 1941 Heitz et a1. May 25, 1948 15 Number 8 FOREIGN PATENTS Country Date Norway "Nov. 15, 1920 Norway Mar. 4, 1940 France Jan. 29, 1906 OTHER REFERENCES A. P. C. publication Sex. No. 345,235, April 20, 

1. A PROCESS OF PRODUCING PERCHLORETHYLENE WHICH COMPRISES BURNING AN INTIMATE MIXTURE OF ACETYLENE AND CHLORINE IN THE PROPORTION BY VOLUME OF ABOUT 1:3 TO 1:3.5, IN THE FORM OF A FLAME IN WHICH FLAME THE TEMPERATURE AT THE COOLER END IS ABOUT 600* C., AND THE TEMPERATURE AT THE HOTTEST PART OF THE FLAME, I.E. AT ITS END, IS ABOUT 750* C. TO ABOUT 950* C. 